In the past, stepping motors have been used to position a lens barrel and associated lens in medical positioning apparatus. The problem with a stepping motor with position feedback is that is operates too slowly for most applications. Applicant's invention replaces a stepping motor with a voice coil actuator with integrated position sensing. The voice coil allows for a faster response and thus shorter equipment use time when performing a procedure.
Generally voice coil actuators do not have position feedback sensing capabilities. Voice coil actuators are generally available in either the moving magnet or moving coil type. The moving coil actuators are also referred to as voice coils.
Typical Linear Voltage Displacement Transducers (“LVDT”) have a means to alter the position of the magnetic core. The LVDT converts rectilinear motion of an object to which it is coupled mechanically into a corresponding electrical signal. LVDT linear position sensors can very accurately measure movements as small as a few millionths of an inch up to several inches. The moving element of an LVDT is a separate tube, which is free to move axially in the LVDT's hollow bore and is mechanically coupled to the object whose position is being measured.
In operation, the LVDT's primary winding is energized by alternating current, also called the primary excitation. The LVDT's electrical output signal is the differential AC voltage between the two secondary windings, which varies with the axial position of the core within the LVDT coil.
Applicant's invention places a voice coil adjacent to and in linear alignment with an LVDT sensor. The voice coil provides accurate armature position sensing. The voice coil actuator has a moving magnet armature which contains the magnetic core required for the LVDT. Applicant provides a hole through the center of the voice coil and LVDT to allow a laser beam to pass through the voice coil and LVDT. There is a core tube or moving armature that passes through the voice coil and LVDT and which has a lens adapter and lens at one end. By accurately moving and positioning the moving armature, the laser beam can be quickly and accurately focused through the lens.